1. Field of the Invention
This invention relates to the field of electronic circuits and devices, and in particular to a circuit and device that provides a low-power, low-cost, on/off control for power supplies within devices, with configurable delay characteristics.
2. Description of Related Art
Most switches that control the application of power within a device are mechanical contact switches that connect a battery or other power source to a power supply, such as a voltage regulated supply.
Complex electronic devices, such as computers, include electronic on/off control switches, wherein the mechanical switch that a user operates provides an input to an electronic circuit, and this electronic circuit provides the connection between the power source and the device""s power supply. In this manner, other control schemes can be used to provide on/off control, by providing other inputs to the electronic circuit. These on/off control circuits also often provide a delayed turn-off, which require the depression of the mechanical on/off switch for an extended duration before power is disconnected from the device, to avoid inadvertent power shut-offs which could cause the loss of data. Providing a delayed turn-off is a fairly simple design task, because while the device is turned on, power is available for running timer circuits, activating shutdown procedures, and so on.
A common problem in portable, low-power, devices is the unintentional turn-on of the device, when the user inadvertently activates a mechanical switch, which can substantially shorten the useful battery life. The useful battery life can also be shortened by unintentionally leaving the device turned on after use. Another problem is the over-use, or over-frequent use, of the on/off switch, because the frequent application and removal of power causes undue stress on the components within the device, causing premature failure.
Timing circuits, similar to those used in conventional on/off control circuits, can be used to provide a delayed turn-on of the device, to prevent unintentional activations, but such circuits require active components that will consume power, particularly during each unintentional activation. Also, the cost of conventional on/off control switches often precludes their use in low-cost devices, or low-profit-margin devices, such as cellular telephones.
It is an object of this invention to provide an on/off control circuit that reduces the likelihood of inadvertent turn-on of a device. It is a further object of this invention to provide an on/off control circuit that draws minimal current in the quiescent state. It is a further object of this invention to provide an on/off control circuit that is usable by other functional elements within the device being controlled. It is a further object of this invention to provide an on/off control circuit that minimizes the stress on components within the circuit, and within the device being controlled.
These objects, and others, are achieved using a variety of techniques designed to optimize the effectiveness of an on/off control circuit. The effectiveness of the on/off control circuit is optimized with regard to cost, power consumption, component life, and utility. An R-C circuit is used to provide a time-delayed turn-on, and turn-off, of the device being controlled, accompanied by a latch that retains the on/off state and controls the coupling of a power source to the device being controlled. The latch is configured as a data flip-flop (DFF) with a clocking signal that is controlled by the time-delayed switch input. The flip-flop has an inverted output signal as its input, thereby providing a toggled on/off operation. The latch also includes an independent reset input, thereby allowing an independent turn-off operation by power management controllers within the device being controlled. In the quiescent state, the preferred embodiment consumes less than half a microWatt of power.